SAN FRANCISCO — THOSE of us who live in the United States are fortunate; generally we don’t have to give a lot of thought to the safety of our tap water. This makes our collective experience with water very different from that of hundreds of millions of people across the globe who lack access to clean water.

But twice this year the water supply for a major American city was interrupted for days by water pollution. In January, a chemical used in the processing of coal leaked from a ruptured storage tank into the Elk River, contaminating the water supply for about 300,000 people in and around Charleston, W.Va., the state’s capital and largest city. Then, last weekend, the water supply for over 400,000 people in Toledo, Ohio, was declared unsafe because of the presence of microcystin, a toxin released by algae blooms in nearby Lake Erie, the source of the city’s water.

While the circumstances in each situation are different, there are notable similarities. In each case, the pollution could not be adequately treated by the local water plants. Sudden “do not drink” (and, in some cases, “do not bathe”) warnings resulted. And in each case, activities in or near the communities caused, or partially caused, the problem. In Charleston, it was an upstream industrial spill; in Toledo, polluted runoff, including from agriculture, along the Great Lakes stoked the slimy, fluorescent algae blooms that sent residents flocking to supermarkets for bottled water.

Those events offer two important reminders about water in the United States.

The first is that while our country has made huge strides in reducing water pollution since the 1970s, when Congress passed federal laws like the Clean Water Act and the Safe Drinking Water Act, controlling water pollution is not a “set it and forget it” endeavor. Those statutes set broad goals but depend on states and the Environmental Protection Agency to design and update programs to keep the water clean.

Charleston underscores the imperative of ensuring that clean water policies are fully implemented and strengthened where necessary. Toledo reminds us that threats are not static and neither is the environment. Polluted runoff was not a primary focus in 1970, and the consequences of climate change were not considered then. But now we recognize that runoff from farms, lawns, streets and parking lots is a major problem across the country and more difficult to control because of its ubiquity. And we also now know that climate change doesn’t just warm the air, it can warm water — resulting in more algae blooms.

A second takeaway is that while the current drought gripping parts of the nation can make us think water scarcity is a function of the absolute quantity of water available, practically speaking it is actually a function of quantity and quality. Toledo was without potable water for several days even though it sits beside the Great Lakes, the largest surface freshwater system on earth.

So what should we do?

There are specific steps that would make a difference, including providing water utilities with broader authority to address threats found in watershed surveys; beefing up pollution prevention requirements for chemical tanks to include uniform rules for storage of hazardous substances; and updating outmoded state and federal rules on runoff to include clear reduction targets, which are lacking today.

Equally important, because almost all of us live downstream of somewhere, uncertainty created by a set of Supreme Court decisions about whether all of the nation’s waters are protected by the Clean Water Act needs to be resolved so that upstream pollution doesn’t cause downstream havoc.

Actions like these will almost certainly need to be paired with an increase in financing. The Environmental Protection Agency says the capital needs of water utilities over 20 years amount to $384 billion to keep tap water clean and another $298 billion to address waste water and runoff. By comparison, over the last 25 years, the E.P.A.’s primary wastewater grant and loan program distributed over $100 billion, a fraction of the investment the nation needs to make now.

Just as important, this moment also calls for a change in thinking about how we can best achieve our nation’s clean water goals. Traditionally, water policy has dealt with issues of quality and quantity separately. This approach must be replaced by an integrated strategy that addresses both together. Neither plentiful, polluted water nor scarce, clean water will meet our needs.

The “green infrastructure” movement taking hold across the nation includes a water management approach that uses natural systems like wetlands and green buffers to reduce runoff, enhance water supply and improve community aesthetics. We need more of this kind of integration and the thinking that animates it.

When we ignore the weaknesses in our current approaches to safeguarding our drinking water supplies, we take a significant risk. If the sudden absence of drinking water in Charleston and Toledo serves to refocus the country on the importance of protecting water with a seriousness that reflects its indispensability, that will be a very good thing.

The Lake George Water Quality

Yesterday afternoon I was at Gull Bay on Lake George with friend, mentor and colleague, Jeff Lape.

According to the NYS Federation of Lake Associations (http://www.nysfola.org/), Lake George is one of the clearest in New York, with a Secchi disk reading as low was 37 feet below the surface.  Uber clear!  The lake also gets high marks for high drinking water quality.